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- /*
- * Copyright (c) Ian F. Darwin 1986-1995.
- * Software written by Ian F. Darwin and others;
- * maintained 1995-present by Christos Zoulas and others.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the above copyright
- * notice immediately at the beginning of the file, without modification,
- * this list of conditions, and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- * notice, this list of conditions and the following disclaimer in the
- * documentation and/or other materials provided with the distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
- * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
- * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
- * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
- * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
- * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
- * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
- * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
- */
- /*
- * is_tar() -- figure out whether file is a tar archive.
- *
- * Stolen (by the author!) from the public domain tar program:
- * Public Domain version written 26 Aug 1985 John Gilmore (ihnp4!hoptoad!gnu).
- *
- * @(#)list.c 1.18 9/23/86 Public Domain - gnu
- *
- * Comments changed and some code/comments reformatted
- * for file command by Ian Darwin.
- */
- #include "file.h"
- #ifndef lint
- FILE_RCSID("@(#)$File: is_tar.c,v 1.43 2018/10/15 16:29:16 christos Exp $")
- #endif
- #include "magic.h"
- #include <string.h>
- #include <ctype.h>
- #include "tar.h"
- #define isodigit(c) ( ((c) >= '0') && ((c) <= '7') )
- private int is_tar(const unsigned char *, size_t);
- private int from_oct(const char *, size_t); /* Decode octal number */
- static const char tartype[][32] = { /* should be equal to messages */
- "tar archive", /* found in ../magic/Magdir/archive */
- "POSIX tar archive",
- "POSIX tar archive (GNU)", /* */
- };
- protected int
- file_is_tar(struct magic_set *ms, const struct buffer *b)
- {
- const unsigned char *buf = CAST(const unsigned char *, b->fbuf);
- size_t nbytes = b->flen;
- /*
- * Do the tar test first, because if the first file in the tar
- * archive starts with a dot, we can confuse it with an nroff file.
- */
- int tar;
- int mime = ms->flags & MAGIC_MIME;
- if ((ms->flags & (MAGIC_APPLE|MAGIC_EXTENSION)) != 0)
- return 0;
- tar = is_tar(buf, nbytes);
- if (tar < 1 || tar > 3)
- return 0;
- if (mime == MAGIC_MIME_ENCODING)
- return 1;
- if (file_printf(ms, "%s", mime ? "application/x-tar" :
- tartype[tar - 1]) == -1)
- return -1;
- return 1;
- }
- /*
- * Return
- * 0 if the checksum is bad (i.e., probably not a tar archive),
- * 1 for old UNIX tar file,
- * 2 for Unix Std (POSIX) tar file,
- * 3 for GNU tar file.
- */
- private int
- is_tar(const unsigned char *buf, size_t nbytes)
- {
- const union record *header = (const union record *)(const void *)buf;
- size_t i;
- int sum, recsum;
- const unsigned char *p, *ep;
- if (nbytes < sizeof(*header))
- return 0;
- recsum = from_oct(header->header.chksum, sizeof(header->header.chksum));
- sum = 0;
- p = header->charptr;
- ep = header->charptr + sizeof(*header);
- while (p < ep)
- sum += *p++;
- /* Adjust checksum to count the "chksum" field as blanks. */
- for (i = 0; i < sizeof(header->header.chksum); i++)
- sum -= header->header.chksum[i];
- sum += ' ' * sizeof(header->header.chksum);
- if (sum != recsum)
- return 0; /* Not a tar archive */
- if (strncmp(header->header.magic, GNUTMAGIC,
- sizeof(header->header.magic)) == 0)
- return 3; /* GNU Unix Standard tar archive */
- if (strncmp(header->header.magic, TMAGIC,
- sizeof(header->header.magic)) == 0)
- return 2; /* Unix Standard tar archive */
- return 1; /* Old fashioned tar archive */
- }
- /*
- * Quick and dirty octal conversion.
- *
- * Result is -1 if the field is invalid (all blank, or non-octal).
- */
- private int
- from_oct(const char *where, size_t digs)
- {
- int value;
- if (digs == 0)
- return -1;
- while (isspace((unsigned char)*where)) { /* Skip spaces */
- where++;
- if (digs-- == 0)
- return -1; /* All blank field */
- }
- value = 0;
- while (digs > 0 && isodigit(*where)) { /* Scan til non-octal */
- value = (value << 3) | (*where++ - '0');
- digs--;
- }
- if (digs > 0 && *where && !isspace((unsigned char)*where))
- return -1; /* Ended on non-(space/NUL) */
- return value;
- }
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